January 27, 19 16] 



NATURE 



597 



ment which he desig-ned with such careful atten- 

 tion to detail for the fundamental astronomy of 

 position in the southern hemisphere. And finally 

 there is a volume, or part of a volume, containing 

 a fine series of measures with the heliometer, the 

 instrument with which Gill's reputation as a 

 practical observer is associated. The reductions 

 in this case have been made by the present pro- 

 fessor of astronomy at Leyden, and illustrate Gill's 

 remarkable power of attracting young and 

 talented astronomers to a distant observatory and 

 enlisting collaboration from outside in the schemes 

 which he had at heart. 



The present instalment of the Astrographic 

 Catalogue bears the date 1914. Since the first 

 volume is dated 191 3, and each contains nearly 

 a tenth of the w^hole share allotted to the Cape 

 Observatory, it may be surmised that the pub- 

 lication of the whole will l^e completed towards 

 the year 1925. With some allowance for pre- 

 liminary work, this means that about thirty years 

 will have been spent in carrying out the project. 

 Two observatories, Greenwich and Oxford, have 

 already finished and published their sections. If 

 this appears to imply that the Cape Observatory 

 has been dilatory, it is fair to notice that the 

 portion undertaken at the Cape is about 30 per 

 cent, in excess of the average ; that it was neces- 

 sary to observe the reference stars simultaneously 

 with the meridian circle ; and that an extremely 

 high standard of accuracy has been aimed at and 

 probably attained. It is also quite possible that 

 in spite of the apparent delay the Cape Observa- 

 tory will be the third to finish. If this be con- 

 firmed by the event, the first three observatories 

 to accomplish their task will all be British. This 

 may prove to be the only satisfactory feature in 

 an undertaking which bids fair to be a dismal 

 failure in the field of international co-operation. 



One feature presents itself at a casual glance 

 through the catalogue. On the whole, the 

 number of stars per plate is very high. But the 

 run of the numbers is far from regular, and can 

 scarcely correspond with real variations of the 

 star density in the sky. The minimum magni- 

 tude recorded on a plate is not constant. This 

 is confirmed by the result of comparing each 

 plate with the overlapping plates, which often 

 shows that the majority of the stars on one plate 

 are unrecorded in the contiguous zones. It is 

 not, of course, a defect peculiar to the Cape 

 plates, though perhaps more conspicuous here 

 because no indication is given of the magnitude 

 scale, and because those stars are marked which 

 are missing in the overlapping zones. It is a 

 small point, doubtless, and the irregularity could 

 scarcely have been avoided. But it illustrates the 

 wisdom of the conference, which, starting out 

 with the avowed object of securing a certain 

 minimum magnitude, laid down a hard and fast 

 rule defining the times of exposure without any 

 regard to the quality of the night or the speed 

 of the plates. As a matter of fact, the sensitive- 

 ness of the plates used has probably increased 

 bv at least one magnitude since the rule was 

 formulated. Thereby, as though the work had 

 NO. 2413, VOL. q6] 



not palpably overtaxed the resources of most 

 of the observatories already, the labour and ex- 

 pense have been augmented in two ways, first 

 by the increase in the number of star images, 

 and then by the supposed need of revising earlier 

 plates in order to conform with the higher 

 numerical standard. When all is said and done, 

 the limiting magnitude on any given astrographic 

 plate is practically an undetermined quantity. 



The volume dealing with the meridian observa- 

 tions made during the years 1905-8 contains much 

 descriptive and tabular matter chiefly of interest 

 to the specialist. The individual results obtained 

 with the new reversible transit-circle and given 

 here will be ultimately combined to form a funda- 

 mental catalogue. Most of the work done with 

 the older instrument was carried out at the 

 request of the late Prof. Boss, and has already 

 appeared in catalogue form. A further list of 

 381 miscellaneous stars is now published in the 

 same form. The individual observations of both 

 lists will be found in this volume. 



The heliometer observations of Jupiter's satel- 

 lites, to the discussion of which the first part of 

 vol. xii. of the Cape Annals is devoted, were made 

 chiefly by Gill and on a few nights by Finlay in 

 the autumn of 1891. They connect satellite with 

 satellite, and do not involve the limb of the 

 planet, the observation of which entails a lower 

 order of accuracy. The main object in view was 

 a determination of the mass of Jupiter, and this 

 requires a most accurate knowledge of the scale 

 value, to which the most careful attention was 

 given. Corrections to all the elements of the 

 satellites, except the mean motions, are involved, 

 and no fewer than twenty-nine quantities enter 

 into the, final equations of condition. Duplicate 

 solutions were made, one under the supervision of 

 Mr. Hough, the other with difi"erent treatment by 

 Prof, de Sitter. As regards the mass of Jupiter 

 the final result is 



i/io47'5o + 'o6. 

 Compared with the best results previously ob- 

 tained, this value of the denominator seems a 

 little high. H. C. P. 



THE CLOSING OF MUSEUMS. 



ACCORDING to the Secretary to the Treasury, 

 "His Majesty's Government are of opinion 

 that the following museums and galleries should 

 be closed to the public : British Museum, Natural 

 History Museum, Science Museum, Geological 

 Museum, Bethnal Green Museum, Tate Gallery, 

 National Portrait Gallery, Wallace Collection, 

 London Museum." The precise sense of the word 

 " should " will appear from events. At any rate, 

 the decision has been made definite in the case of 

 all departments of the British Museum except the 

 reading-room, but the National Gallery and the 

 Victoria and Albert Museum are not to be 

 closed. 



This decision will come as a severe blow to 

 those who have been urging the need of a greater 

 regard for science and education, but, in view of 



